CN115336054A - Method for operating fuel cell - Google Patents

Method for operating fuel cell Download PDF

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CN115336054A
CN115336054A CN202180024452.1A CN202180024452A CN115336054A CN 115336054 A CN115336054 A CN 115336054A CN 202180024452 A CN202180024452 A CN 202180024452A CN 115336054 A CN115336054 A CN 115336054A
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fuel cell
gas
electrolyte membrane
operating
membrane
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坂上智洋
出原大辅
桥本胜
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Toray Industries Inc
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Toray Industries Inc
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
    • H01M8/04701—Temperature
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/9075—Catalytic material supported on carriers, e.g. powder carriers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
    • H01M4/90—Selection of catalytic material
    • H01M4/92—Metals of platinum group
    • H01M4/925—Metals of platinum group supported on carriers, e.g. powder carriers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
    • H01M8/04746—Pressure; Flow
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
    • H01M8/04746—Pressure; Flow
    • H01M8/04753—Pressure; Flow of fuel cell reactants
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
    • H01M8/04828—Humidity; Water content
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/04—Auxiliary arrangements, e.g. for control of pressure or for circulation of fluids
    • H01M8/04298—Processes for controlling fuel cells or fuel cell systems
    • H01M8/04694—Processes for controlling fuel cells or fuel cell systems characterised by variables to be controlled
    • H01M8/04828—Humidity; Water content
    • H01M8/04835—Humidity; Water content of fuel cell reactants
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1004—Fuel cells with solid electrolytes characterised by membrane-electrode assemblies [MEA]
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1007—Fuel cells with solid electrolytes with both reactants being gaseous or vaporised
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
    • H01M8/1018—Polymeric electrolyte materials
    • H01M8/102—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer
    • H01M8/1023—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer having only carbon, e.g. polyarylenes, polystyrenes or polybutadiene-styrenes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
    • H01M8/1018—Polymeric electrolyte materials
    • H01M8/102—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer
    • H01M8/1025—Polymeric electrolyte materials characterised by the chemical structure of the main chain of the ion-conducting polymer having only carbon and oxygen, e.g. polyethers, sulfonated polyetheretherketones [S-PEEK], sulfonated polysaccharides, sulfonated celluloses or sulfonated polyesters
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M8/1016—Fuel cells with solid electrolytes characterised by the electrolyte material
    • H01M8/1018—Polymeric electrolyte materials
    • H01M8/1067—Polymeric electrolyte materials characterised by their physical properties, e.g. porosity, ionic conductivity or thickness
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M8/00—Fuel cells; Manufacture thereof
    • H01M8/10—Fuel cells with solid electrolytes
    • H01M2008/1095—Fuel cells with polymeric electrolytes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0065—Solid electrolytes
    • H01M2300/0082—Organic polymers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/30—Hydrogen technology
    • Y02E60/50—Fuel cells

Abstract

The invention provides a method for operating a fuel cell, in which a polymer electrolyte membrane can be sufficiently humidified even under high temperature conditions, and excellent power generation performance can be obtained. The present invention is a method for operating a fuel cell including a membrane electrode assembly having an electrolyte membrane, a catalyst layer, and a gas diffusion layer, the method comprising a step of setting an operating temperature of the fuel cell to 100 ℃ or higher, wherein a relative humidity of a supply gas supplied to the fuel cell is set to 70% or higher, and a back pressure of the supply gas is set to 330kPa or higher.

Description

Method for operating fuel cell
Technical Field
The present invention relates to a method for operating a fuel cell including a membrane electrode assembly having an electrolyte membrane, a catalyst layer, and a gas diffusion layer, and capable of obtaining excellent power generation performance even under high temperature conditions by increasing the humidity and back pressure of supplied gas during high temperature operation.
Background
A fuel cell is a power generation device that extracts electric energy by electrochemically oxidizing a fuel such as hydrogen or methanol, and has recently been drawing attention as a clean energy supply source. Among them, since the polymer electrolyte fuel cell has a standard operating temperature as low as about 100 ℃ and a high energy density, it is expected to be widely used as a power generation device for a small-scale distributed power generation facility, a mobile body such as an automobile or a ship. In addition, the battery has attracted attention as a power source for small-sized mobile devices and portable devices, and is expected to be mounted on mobile phones, personal computers, and the like, in place of secondary batteries such as nickel hydride batteries and lithium ion batteries.
A polymer electrolyte fuel cell is generally configured such that a gas diffusion layer for supplying fuel gas and oxidizing gas to a catalyst layer, a catalyst layer of an anode and a cathode for generating a reaction responsible for power generation, and a polymer electrolyte membrane serving as a proton conductor between the anode catalyst layer and the cathode catalyst layer constitute a membrane electrode assembly (hereinafter, may be simply referred to as MEA), and a unit cell in which the MEA is sandwiched by separators is used as a unit.
First, the polymer electrolyte membrane is required to have high proton conductivity, and particularly, high proton conductivity is required even under high-temperature and low-humidity conditions. Nafion (registered trademark) (manufactured by dupont) which is a perfluorosulfonic acid polymer has been widely used for a polymer electrolyte membrane. Nafion (registered trademark) exhibits high proton conductivity through proton conduction channels generated by the cluster structure, while proton conductivity under low humidification conditions is problematic.
On the other hand, in recent years, hydrocarbon-based polymer electrolyte membranes which can replace Nafion (registered trademark) have been actively developed, and among these, in particular, in order to improve proton conductivity, several attempts have been made to form a microphase-separated structure using a block copolymer composed of a hydrophobic segment and a hydrophilic segment, but proton conductivity under low humidity conditions is still a problem. In view of such circumstances, in a fuel cell, it becomes important to manage water (particularly, the water content of an electrolyte membrane) in a membrane electrode assembly.
On the other hand, in order to further improve the performance of the polymer electrolyte fuel cell, it is required to increase the operating temperature to more than 100 ℃. The increase in the operating temperature improves the catalytic activity and the power generation performance, and the increase in the heat removal efficiency of the radiator enables the fuel cell system to be downsized. In addition, catalyst poisoning by poisoning sources such as carbon monoxide contained in the fuel gas can be reduced, and performance degradation due to impurities can be suppressed. However, there is a problem that sufficient performance cannot be obtained because dehydration from the membrane electrode assembly, particularly the electrolyte membrane, occurs due to an increase in the operating temperature and proton conductivity is reduced. Therefore, development of an electrolyte membrane material that can be used at high temperatures, particularly in a temperature range exceeding 100 ℃, and an operable fuel cell system have been advanced.
Patent document 1 describes a separator structure for suppressing an increase in pressure loss of gas and a pressure difference between an anode and a cathode as a cell structure of a polymer electrolyte fuel cell operating at a high temperature of 100 ℃. Among them, there is disclosed a structure in which the sectional area of a flow path on the downstream side in the gas flow direction of a cathode separator is made larger than that on the upstream side, thereby reducing the pressure loss of the cathode separator and improving the energy efficiency.
Patent document 2 describes a membrane-electrode assembly for a polymer electrolyte fuel cell, which has a proton conductive membrane that has high proton conductivity, is less likely to swell even under high-temperature and high-humidity conditions, and has excellent dimensional stability. It is disclosed therein that a structure of a membrane-electrode structure is provided in which a dimensional change is small even at a high sulfonic acid equivalent by using a branched polyarylene copolymer having a specific structural unit as an electrolyte membrane.
Further, patent document 3 describes a high-temperature polymer electrolyte membrane fuel cell that operates substantially independently of water in the fuel cell, and an operating method thereof. In order to operate in a state substantially independent of moisture, a method is disclosed in which an electrolyte in which a self-dissociating compound such as phosphoric acid is held in a membrane is used, the operating temperature is 80 to 300 ℃, and the operating pressure is 0.3 to 5bar, thereby reducing the influence of the CO concentration in the process gas and the amount of moisture present in the battery.
Documents of the prior art
Patent document
Patent document 1, japanese patent laid-open No. 2007-115413
Patent document 2 Japanese patent laid-open No. 2009-238468
Patent document 3 Japanese patent application laid-open No. 2003-504805
Disclosure of Invention
Problems to be solved by the invention
However, the present inventors have found that if the amount of humidification is increased to maintain proton conductivity during high-temperature operation in a membrane electrode assembly using the solid polymer electrolyte membrane described in patent documents 1 and 2, the amount of moisture in the feed gas increases, and the concentration of the reactant gas, particularly the oxidizing gas, decreases, and the substance diffusion resistance increases, resulting in a decrease in performance. In this connection, there is no mention in any document.
In addition, the electrolyte described in patent document 3 may be strongly poisoned by a catalyst due to its strong acidity, and may lower the power generation performance in a high temperature region. Further, it is also a problem that proton conductivity is reduced with use thereof. Therefore, in order to maintain high power generation performance in a high temperature region, it is necessary to appropriately humidify an electrolyte using a solid polymer type polymer in which a self-dissociable compound such as phosphoric acid is not contained in the membrane, and to suppress a decrease in the concentration of a reaction gas in the vicinity of an electrode.
In view of the background of the prior art described above, the present invention provides a method for operating a fuel cell in which a polymer electrolyte membrane can be sufficiently humidified even under high-temperature conditions, and excellent power generation performance can be obtained.
Means for solving the problems
In order to solve the problem, the present invention adopts the following method.
That is, the method for operating a fuel cell according to the present invention is a method for operating a fuel cell including a Membrane Electrode Assembly (MEA) having an electrolyte membrane, a catalyst layer, and a gas diffusion layer, and includes a step of setting an operating temperature of the fuel cell to 100 ℃ or higher, wherein a relative humidity of a supply gas supplied to the fuel cell in the step is set to 70% or higher, and a back pressure of the supply gas is set to 330kPa or higher.
A fuel cell system according to the present invention is a fuel cell system used in the method for operating a fuel cell according to the present invention, and includes a fuel cell having a membrane electrode assembly including an electrolyte membrane, a catalyst layer, and a gas diffusion layer, a humidifier for humidifying supply gas to be supplied to the fuel cell, and a compressor for increasing a back pressure of the supply gas.
Effects of the invention
According to the present invention, it is possible to provide a method of operating a fuel cell having high power generation performance under high temperature conditions.
Drawings
Fig. 1 is a schematic cross-sectional view for explaining a method of manufacturing a membrane electrode assembly manufactured in example 1 of the present invention.
Fig. 2 is a schematic cross-sectional view for explaining a method of manufacturing a membrane electrode assembly manufactured in example 2 of the present invention.
Fig. 3 is a perspective view for explaining the structure of a fuel cell unit of the present invention.
Fig. 4 is a schematic diagram for explaining a fuel cell system of the present invention.
Detailed Description
The present invention will be described in detail below.
[ Membrane electrode Assembly ]
A Membrane Electrode Assembly (MEA) of the present invention has an electrolyte membrane, catalyst layers provided on both sides of the electrolyte membrane, and a gas diffusion layer provided in contact with the catalyst layers on the side opposite to the electrolyte membrane.
(electrolyte Membrane)
The electrolyte membrane contained in the membrane electrode assembly of the present invention is not particularly limited, but is preferably an electrolyte membrane containing a solid polymer electrolyte, and the solid polymer electrolyte is preferably an electrolyte containing a proton conductive polymer.
In the present invention, as the proton conductive polymer, a perfluorosulfonic acid polymer which has been widely used as a polymer electrolyte membrane can be used, but a polymer electrolyte membrane containing a hydrocarbon polymer which has been actively developed in recent years is preferably used. The polymer electrolyte membrane containing a hydrocarbon polymer is an electrolyte membrane that can be used in place of a perfluorosulfonic acid polymer because it is inexpensive, suppresses fuel crossover, has excellent mechanical strength, has a high softening temperature, and is resistant to high temperatures.
Among these, in order to improve the low wet proton conductivity, there have been several attempts to form a microphase-separated structure using a block copolymer composed of a hydrophobic segment and a hydrophilic segment. By using a polymer having such a structure, the mechanical strength is improved by hydrophobic interaction or aggregation between hydrophobic segments, and the proton conductivity is improved by clustering due to electrostatic interaction between ionic groups of hydrophilic segments, and the like, and by forming ion conductive paths.
As mechanisms by which protons move in these electrolyte membranes, an on-vehicle mechanism by which hydrogen ions themselves move after proton hydration (12499125401246312523). Under low humidification conditions with few water molecules, the hopping movement of the sulfonic acid group based on the on-vehicle hydrated proton mechanism dominates.
In this case, in the case of a fluorine-based electrolyte membrane or the like, since the acid dissociation constant of the sulfonic acid group contained in the molecular structure is small and the proton is easily dissociated, the proton conduction by hopping is easily performed. On the other hand, in a polymer electrolyte membrane containing a hydrocarbon polymer, since the acid dissociation constant of sulfonic acid groups in the molecule is larger than that of a fluorine electrolyte membrane and dissociation of protons is difficult to occur, the decrease in proton conductivity under low humidity conditions is larger than that of a fluorine electrolyte membrane. The acid dissociation constant as used herein is one of indexes for indicating the acid strength of a certain substance, and is represented by the negative common logarithm pKa of the equilibrium constant in a dissociation reaction in which a proton is released from an acid.
In the present invention, the hydrocarbon polymer is preferably an aromatic hydrocarbon polymer. Specific examples of the aromatic hydrocarbon polymer include polysulfone having an aromatic ring in the main chain, polyethersulfone, polyphenylene ether, polyarylether polymer, polyphenylene sulfide sulfone, polyparaphenylene, polyarylene polymer, polyarylene ketone, polyether ketone, polyarylene phosphine oxide, polyether phosphine oxide, polybenzo-polymer, and the like
Figure BDA0003863314970000051
And polymers such as oxazoles, polybenzothiazoles, polybenzimidazoles, aromatic polyamides, polyimides, polyetherimides, polyimide sulfones, and the like.
Further, "polyether sulfone" is a generic name of polymers having an ether bond and a sulfone bond in the molecular chain thereof. "polyetherketone" is a generic term for a polymer having ether bonds and ketone bonds in its molecular chain, and includes polyetherketoneketone, polyetheretherketone, polyetheretherketoneketone, polyetherketoneetherketoneketone, polyetherketonesulfone, and the like, and is not limited to a specific polymer structure.
Among these aromatic hydrocarbon-based polymers, polymers such as polysulfone, polyethersulfone, polyphenylene ether, polyarylether-based polymer, polyphenylene sulfide sulfone, polyaryl ketone, polyetherketone, polyarylene phosphine oxide, and polyether phosphine oxide are preferable, and polyether ketone is more preferable, from the viewpoint of mechanical strength, physical durability, processability, and hydrolysis resistance. As the polyether ketone, a block copolymer composed of a segment having a benzophenone structure having an ionic group and a segment having a dioxolane structure is more preferable.
The method for synthesizing the aromatic hydrocarbon polymer is not particularly limited as long as the above properties and requirements can be satisfied. As such a method, a method described in Journal of Membrane Science,197, 2002, p.231-242, for example, can be used.
For example, preferred polymerization conditions for synthesizing an aromatic hydrocarbon polymer by a polycondensation reaction are as follows. The polymerization can be carried out at a temperature in the range of 0 to 350 ℃ but preferably at a temperature of 50 to 250 ℃. When the temperature is lower than 0 ℃, the reaction tends to be insufficient, and when the temperature is higher than 350 ℃, the decomposition of the polymer tends to start. The reaction is preferably carried out in a solvent. Examples of the solvent that can be used include, but are not limited to, aprotic polar solvents such as N, N-dimethylacetamide, N-dimethylformamide, N-methyl-2-pyrrolidone, dimethylsulfoxide, sulfolane, 1, 3-dimethyl-2-imidazolidinone, hexamethylphosphoric triamide, and the like, as long as the solvent can be used as a stable solvent in the aromatic nucleophilic substitution reaction. These organic solvents may be used alone or as a mixture of 2 or more.
When the condensation reaction is carried out in a solvent, it is preferable to mix the monomers so that the concentration of the obtained polymer is 5 to 50% by weight. When the polymer concentration is less than 5% by weight, the polymerization degree tends to be difficult to increase. On the other hand, when the polymer concentration is more than 50% by weight, the viscosity of the reaction system becomes too high, and the post-treatment of the reaction product tends to be difficult.
In the present invention, the aromatic hydrocarbon-based polymer may have an ionic group. Examples of the method for introducing an ionic group into an aromatic hydrocarbon polymer include a method of polymerizing a monomer having an ionic group and a method of introducing an ionic group into a polymer reaction. As a method for carrying out polymerization using a monomer having an ionic group, a monomer having an ionic group in a repeating unit may be used, and a suitable protecting group may be introduced as needed, and polymerization may be carried out, followed by deprotection.
Examples of the method of introducing an ionic group include a method of sulfonating an aromatic ring, that is, a method of introducing a sulfonic acid group, and examples thereof include methods described in Japanese patent application laid-open Nos. 2-16126 and 2-208322.
Specifically, for example, the aromatic ring can be sulfonated by reacting it with a sulfonating agent such as chlorosulfonic acid in a solvent such as chloroform, or by reacting it with concentrated sulfuric acid or fuming sulfuric acid. The sulfonating agent is not particularly limited as long as it can sulfonate the aromatic ring, and sulfur trioxide and the like may be used in addition to the above. When the aromatic ring is sulfonated by this method, the degree of sulfonation can be easily controlled depending on the amount of the sulfonating agent used, the reaction temperature and the reaction time. The introduction of the sulfonimide group into the aromatic polymer can be achieved by, for example, a method of reacting a sulfonic acid group with a sulfonamide group.
The ionic group is preferably a functional group having a negative charge, and particularly preferably a functional group having a proton exchange ability. As such a functional group, a sulfonic acid group, a sulfonimide group, a sulfuric acid group, a phosphonic acid group, a phosphoric acid group, or a carboxylic acid group is preferably used. Here, the sulfonic acid group is a group represented by the following general formula (f 1), the sulfonylimide group is a group represented by the following general formula (f 2) [ general formula (f 2), R represents an arbitrary organic group ], the sulfuric acid group is a group represented by the following general formula (f 3), the phosphonic acid group is a group represented by the following general formula (f 4), the phosphoric acid group is a group represented by the following general formula (f 5) or (f 6), and the carboxylic acid group is a group represented by the following general formula (f 7).
Figure BDA0003863314970000071
The ionic group includes the case where the functional groups (f 1) to (f 7) are salts. As the cation forming the salt, any metal cation, NR4+ (R is any organic group) can be exemplified. The valence of the metal cation is not particularly limited. Specific examples of preferable metal ions include ions of Li, na, K, rh, mg, ca, sr, ti, al, fe, pt, rh, ru, ir, and Pd. Among them, na, K, and Li ions which are inexpensive and easily substituted with protons are preferably used for the block copolymer used in the present invention.
These ionic groups may be contained in the polymer in 2 or more species, and the combination may be appropriately determined depending on the structure of the polymer and the like. Among them, sulfonic acid groups, sulfonimide groups, or sulfuric acid groups are more preferably used from the viewpoint of high proton conductivity, and sulfonic acid groups are most preferably contained from the viewpoint of raw material cost.
The softening temperature of the electrolyte membrane of the present invention is preferably 120 ℃ or higher. If the softening temperature is less than 120 ℃, the mechanical strength of the electrolyte membrane is reduced at operating temperatures exceeding 100 ℃, and deterioration such as creep or membrane rupture may be caused. In order to maintain durability under high temperature conditions, it is preferable to use an electrolyte membrane having a softening temperature of 120 ℃ or higher. In the present invention, the softening temperature is a temperature at which the slope of the storage elastic modulus in the dynamic viscoelasticity measurement of the electrolyte membrane shows an inflection point.
As the polymer electrolyte membrane having such a high softening temperature, a polymer electrolyte membrane containing the above-mentioned hydrocarbon-based polymer is preferably used. The softening temperature of a general perfluorosulfonic acid polymer is around 80 ℃ and the mechanical strength may not be sufficient at an operating temperature exceeding 100 ℃. On the other hand, the softening temperature of the hydrocarbon polymer is higher, and an electrolyte membrane having a softening temperature of 120 ℃ or higher can be easily produced. Thus, a polymer electrolyte membrane made of a hydrocarbon polymer can be more preferably used as an electrolyte membrane included in a fuel cell operated under high temperature conditions.
The electrolyte membrane of the present invention preferably has an oxygen transmission coefficient of 1.0X 10 at 90 ℃ and 80% RH -9 cm 3 ·cm/cm 2 Sec cmHg or less, more preferably 5.0X 10 -10 cm 3 ·cm/cm 2 Sec cmHg or less, more preferably 1.0X 10 -10 cm 3 ·cm/cm 2 Sec cmHg or less. Since the electrolyte membrane has high oxygen permeability, the amount of hydrogen peroxide generated by a chemical reaction between oxygen permeating through the membrane and hydrogen supplied to the counter electrode increases, which causes chemical degradation of the membrane. In particular, under high temperature conditions, the saturated solubility of gas in the electrolyte membrane tends to decrease, but the diffusion rate of gas in the electrolyte membrane is greatly increased, and as a result, the gas permeability coefficient tends to increase. In order to maintain sufficient chemical durability at an operating temperature of more than 100 ℃, the oxygen gas permeability coefficient at 90 ℃, 80% - 9 cm 3 ·cm/cm 2 Sec cmHg or less, the decrease in chemical durability associated with the production of hydrogen peroxide can be suppressed.
The electrolyte membrane of the present invention preferably has a hydrogen gas permeability coefficient of 5.0X 10 at 90 ℃ and 80% RH -9 cm 3 ·cm/cm 2 Sec cmHg or less, more preferably 1.0X 10 -9 cm 3 ·cm/cm 2 Sec cmHg or less. Since the electrolyte membrane has high hydrogen permeability, the amount of hydrogen peroxide generated by a chemical reaction between hydrogen permeating through the membrane and oxygen supplied to the counter electrode, which causes chemical degradation of the membrane, increases. In particular, under high temperature conditions, the saturated solubility of gas to the electrolyte membrane tends to decrease, but the gas permeation coefficient tends to increase because the diffusion rate of gas in the electrolyte membrane increases greatly. In order to maintain sufficient chemical durability at an operating temperature of more than 100 ℃, the hydrogen gas permeability coefficient at 90 ℃ and 80% RH is 5.0X 10 -9 cm 3 ·cm/cm 2 Sec cmHg or less, the decrease in chemical durability associated with the production of hydrogen peroxide can be suppressed.
In the present invention, the gas permeability coefficients of oxygen and hydrogen of the electrolyte membrane at 90 ℃ and 80% RH were measured under the following conditions. The average of the number of tests 3 was calculated as the gas permeability coefficient.
The device comprises the following steps: differential pressure gas transmission rate measuring systems GTR-30AX (manufactured by GTR 1248612412412412412412412463
Temperature × relative humidity: 90 ℃ x 80% RH
Test gas: oxygen and hydrogen
Test gas pressure: the total pressure of the vapor contained therein was 101.3kPa (atmospheric pressure)
90 ℃ and 80% RH, the measured gas partial pressure of each was 45.2kPa
Gas transmission area: 3.14cm 2 (circular sample with diameter of 2.0 cm) masking
Measuring the number of n: 3 (determination using the same sample)
Since the gas permeability coefficient of the electrolyte membrane is easily lowered, the polymer electrolyte used in the present invention is preferably a hydrocarbon polymer. In order to obtain sufficient mechanical strength and gas barrier properties, the polymer electrolyte is preferably an aromatic hydrocarbon polymer having crystallinity. Here, "have crystallinity" means that they have crystallizable properties that can be crystallized at elevated temperatures, or have already been crystallized.
The presence or absence of crystallinity was confirmed by Differential Scanning Calorimetry (DSC) or wide-angle X-ray diffraction. In the present invention, it is preferable that the heat of crystallization after film formation as measured by differential scanning calorimetry is 0.1J/g or more, or the degree of crystallization as measured by wide-angle X-ray diffraction is 0.5% or more. That is, when a crystallization peak is not found in the differential scanning calorimetry, it is considered that the polymer electrolyte is crystallized and the polymer electrolyte is amorphous, but when the polymer electrolyte is crystallized, the crystallinity measured by wide-angle X-ray diffraction is 0.5% or more.
The thickness of the electrolyte membrane is not particularly limited, but when it is thicker than 20 μm, the power generation performance tends to be lowered, and when it is smaller than 5 μm, the durability and the handling property tend to be lowered, and it is preferably 5 μm or more and 20 μm or less. When the electrolyte membrane thickness is less than 5 μm, the amount of water held in the membrane is small, and the membrane is dried at an early stage under high temperature conditions, which may cause a decrease in power generation performance.
(catalyst layer)
The catalyst layer of the present invention is composed of an ion conductor and catalyst-supporting particles that support a catalyst on a carrier. The catalyst is preferably noble metals such as platinum, gold, ruthenium, iridium, etc., which exhibit high activity in oxidation and reduction reactions, but is not limited thereto. As the carrier, carbon particles or oxide particles having conductivity, high chemical stability, and a high surface area are preferable, and metal oxide particles are particularly preferable. Examples of the carbon particles include acetylene black, ketjen black, vulcan carbon, and examples of the metal oxide particles include tin oxide and titanium oxide.
In the present invention, it is particularly preferable to use a chemically stable metal oxide support even in an oxidizing atmosphere of 100 ℃ or higher. The carbon particles are accelerated in oxidation in an oxidizing atmosphere of 100 ℃ or higher, and the catalyst particles supported on the carbon particles may be accelerated in deterioration due to detachment or sintering. By using the metal oxide carrier, the deterioration of the catalyst carrier under high-temperature operation conditions can be suppressed, and high power generation performance can be maintained.
(gas diffusion layer)
The gas diffusion layer of the present invention comprises a carbon sheet and a microporous layer. That is, the carbon sheet can be produced by forming a microporous layer on the carbon sheet.
The microporous layer is composed of a hydrophobic resin such as PTFE and a conductive filler. As the conductive filler, carbon powder is preferable. Examples of the carbon powder include carbon black such as furnace black, acetylene black, lamp black, and thermal cracking carbon black, graphite such as flake graphite, scale graphite, earthy graphite, artificial graphite, expanded graphite, and flake graphite, carbon nanotubes, and milled fibers of linear carbon fibers. Among these, carbon black is more preferably used as the carbon powder as the filler, and acetylene black is preferably used because of less impurities.
In the present invention, from the viewpoint of improving water retention, it is preferable to reduce the amount of the hydrophobic resin used for the microporous layer. Further, by using a hydrophilic resin having adhesive properties instead of a hydrophobic resin, the water retentivity as a membrane electrode assembly can be further improved.
The carbon sheet is important to be porous because of high gas diffusivity for diffusing the gas supplied from the separator into the catalyst layer and high water drainage for discharging the water generated by the electrochemical reaction into the separator. Further, the carbon sheet of the present invention preferably has high conductivity in order to extract generated current. Therefore, in order to obtain the carbon sheet, a porous body having conductivity is preferably used. More specifically, for the porous body used for obtaining the carbon sheet, for example, a porous body containing carbon fibers such as a carbon fiber woven fabric, a carbon paper, and a carbon fiber nonwoven fabric, and a carbonaceous foamed porous body containing carbon fibers are preferably used.
Among these, in order to obtain a carbon sheet, it is preferable to use a porous body containing carbon fibers because of excellent corrosion resistance, and further, to use a carbon sheet in which a carbon fiber paper sheet is bonded with a carbide (binder) because it has excellent characteristics of absorbing dimensional change in a direction perpendicular to the surface of the electrolyte membrane (thickness direction), that is, "spring properties".
(method for producing Membrane electrode Assembly)
The method for manufacturing the Membrane Electrode Assembly (MEA) having the electrolyte membrane, the catalyst layer, and the gas diffusion layer is roughly divided into: (I) A method of producing a Gas Diffusion Electrode (GDE) having a catalyst layer formed on one surface of a gas diffusion layer, and laminating the produced Gas Diffusion Electrode (GDE) and an electrolyte membrane, and (II) a method of producing a catalyst layer-equipped electrolyte membrane (CCM) and laminating the produced electrolyte membrane (CCM) and a gas diffusion layer.
Fig. 2 is a schematic cross-sectional view for explaining the method (I) (the method of example 2 described later).
In the case of the method (I), first, two Gas Diffusion Electrodes (GDEs) are produced in which an anode catalyst layer 2a and a cathode catalyst layer 2b are formed on the microporous layer formation surfaces of an anode gas diffusion layer 1a and a cathode gas diffusion layer 1b, which are gas diffusion layers, respectively. Then, the electrolyte membrane is disposed in direct contact with and joined to the catalyst layer formation surfaces of the anode and cathode gas diffusion electrodes.
Fig. 1 is a schematic cross-sectional view for explaining the method (II) (the method of example 1 described later).
In the case of the method (II), first, a catalyst layer-equipped electrolyte membrane (CCM) is produced in which an anode catalyst layer 2a and a cathode catalyst layer 2b are laminated on both surfaces of an electrolyte membrane 3. Then, the anode and cathode electrode substrates (anode gas diffusion layer 1a and cathode gas diffusion layer 1 b) were placed in direct contact with and joined to the catalyst layer formation surface of the CCM.
The method for joining the electrolyte membrane, the catalyst layer, and the gas diffusion layer is not particularly limited, and known methods (for example, electrochemical (electro chemical) plating method described in 1985,53, p.269, electrochemical association (j.electrochemical. Soc.), electrochemical Science and Technology (Electrochemical Science and Technology), and heat and pressure joining method for gas diffusion electrodes described in 1988, 135, 9, p.2209) can be used.
In the case where the electrolyte membrane, the catalyst layer, and the gas diffusion layer are integrated by pressing, the temperature and pressure thereof are preferably appropriately selected depending on the thickness, water content, and catalyst layer or electrode substrate of the electrolyte membrane. Specific examples of the pressing method include roll pressing with a predetermined pressure or gap, flat pressing with a predetermined pressure, and the like, and these methods are preferably performed in a range of 0 to 250 ℃ from the viewpoints of industrial productivity, suppression of thermal decomposition of a polymer material having an ionic group, and the like. The pressurization is preferably as weak as possible from the viewpoint of protecting the electrolyte membrane or the electrodes, and in the case of a platen press, a pressure of 10MPa or less is preferred. From the viewpoint of preventing short-circuiting between the anode electrode and the cathode electrode, it is also one of preferable options to form a fuel cell unit by stacking the electrode and the electrolyte membrane without performing lamination in the pressing step. In this method, when the fuel cell repeatedly generates power, the electrolyte membrane, which is presumed to be a cause of the short-circuit portion, tends to be inhibited from deteriorating, and the durability as the fuel cell is good.
Specifically, it is preferable to manufacture the MEA by laminating the electrolyte membrane, the gas diffusion layer, and the catalyst layer as shown in fig. 1 and 2 and pressing them at a constant temperature and pressure. Such lamination and pressing may be performed simultaneously on both sides, or may be performed sequentially one on another.
As a method for continuously producing a membrane electrode assembly, there is a method in which a roll-shaped electrolyte membrane is produced, and then the electrolyte membrane is laminated with a catalyst layer and/or a gas diffusion layer, and pressed at a constant temperature and pressure. In the case of laminating a film-like member such as a substrate, an electrolyte membrane, or a substrate-attached electrolyte membrane, it is preferable to perform the lamination while applying a tensile force to each film-like member, and a method of providing a tensile force cutter (124861253171125124125124599. The tension cutter may be provided with a motor, a clutch, a brake, and the like on a roll, and preferably includes a detection mechanism for detecting tension applied to the film. Examples of the roller used in the tension cutter include a nip roller, a suction roller, and a combination of a plurality of rollers. The nip roller nips the film by the roller, and controls the feed speed of the film by the frictional force generated by the nip pressure, and as a result, the pressure applied to the film can be changed before and after the roller. The suction roller sucks the film-shaped member by a negative pressure inside a roller having a plurality of holes on the surface thereof or a roller having a mesh or curtain shape with a yarn wound around the surface thereof, and controls the feeding speed of the film-shaped member by a frictional force generated by the suction force, so that the pressure applied to the film-shaped member can be changed before and after the roller.
[ Fuel cell Unit ]
Fig. 3 is a perspective view for explaining the structure of the fuel cell unit 10 of the present invention.
The membrane electrode assembly 4 produced as described above is joined to the anode separator 5a and the cathode separator 5b to form the fuel cell 10. A plurality of grooves serving as flow paths through which the hydrogen gas 6 passes are formed in the surface of the anode separator 5a that is joined to the anode gas diffusion layer 1 a. The hydrogen gas 6 supplied into the groove of the anode separator 5a reaches the anode catalyst layer 2a through the anode gas diffusion layer 1a for the oxidation reaction. Further, a plurality of grooves serving as flow paths through which air or oxygen 7 passes are formed in the surface of the cathode separator 5b that is joined to the cathode gas diffusion layer 1 b. The air or oxygen 7 supplied into the groove of the anode separator 5b reaches the cathode catalyst layer 2b through the cathode gas diffusion layer 1b for the reduction reaction.
[ Fuel cell System ]
Fig. 4 is a schematic diagram for explaining the fuel cell system 20 of the present invention.
The fuel cell system 20 is mainly composed of the fuel cell stack 11, humidifiers 12a and 12b, compressors 13a and 13b, back pressure valves 14a and 14b, pipes connecting these components, and various sensors. The fuel cells 10 (fig. 3) produced as described above are alternately connected to and integrated with a cooling plate (not shown) to form a fuel cell stack 11.
(humidifier)
The humidifier humidifies the gas supplied to the fuel cell unit. The humidifier is disposed upstream of the gas supply port for supplying gas to the fuel cell stack 11. At this time, by controlling the amount of moisture supplied from the humidifier in accordance with the operating temperature of the fuel cell, the electrolyte membrane can be humidified appropriately regardless of the operating temperature. As the humidification method, a method of passing the supply gas through a water layer containing heated water (bubbling method), a method of directly adding water vapor to the supply gas and mixing it (water vapor addition method), or the like can be used. In the operation method of the present invention, since the operation temperature of the fuel cell exceeds 100 ℃, the gas supplied to the humidifier is also at a high temperature equal to or higher than the same, and therefore, a humidifier that can sufficiently humidify the supplied gas even in a temperature range of 100 ℃ or higher and has high-temperature durability is preferable.
(compressor)
The compressor is used to increase the pressure of the supply gas of the fuel cell unit. The compressor compresses a supply gas, particularly a cathode gas (air or oxygen), and supplies the gas having a high pressure to the fuel cell. The compressor for compressing the cathode gas uses air as the cathode gas, and is disposed between the air intake port and the gas supply port of the fuel cell stack when air is always taken in from the outside of the fuel cell system, and is disposed between the paths from the gas discharge port to the gas supply port in a configuration in which the supply gas is circulated in the fuel cell system.
(Cooling liquid)
The coolant is used to control the operating temperature of the fuel cell unit. The coolant is supplied to the cooling plate by a coolant circulation pump, absorbs heat generated during power generation of the fuel cell stack, and is radiated to a radiator (not shown). In the operation method of the present invention, since the operation temperature of the fuel cell exceeds 100 ℃, and the coolant has a similarly high temperature, the coolant having a low vapor pressure is preferably a coolant that can sufficiently cool the fuel cell stack even in a temperature range of 100 ℃ or higher.
[ method of operating Fuel cell ]
The method for operating a fuel cell according to the present invention includes a step of setting an operating temperature of the fuel cell to 100 ℃ or higher using the fuel cell system, wherein a relative humidity of a supply gas supplied to the fuel cell is set to 70% or higher, and a back pressure of the supply gas is set to 330kPa or higher.
In the present invention, the relative humidity (% RH) refers to a water vapor pressure relative to a saturated water vapor pressure at a certain temperature, and the back pressure refers to a pressure of the supply gas at the outlet of the fuel cell stack. In addition, the pressure in the present invention means an absolute pressure.
A specific operation method of the fuel cell of the present invention will be described below with reference to fig. 4 (fuel cell system 20).
In the present invention, the operating temperature of each fuel cell 10 (fig. 3) in the fuel cell stack 11 is heated to 100 ℃ or higher by heating from the outside of the fuel cell stack 11 using a heater or the like, for example. The temperature of the fuel cell 10 can be set to 100 ℃ or higher by adjusting the heating temperature of a heater or the like while measuring it by a method using a thermocouple embedded in the cell, a method using thermography (infrared temperature imaging device), or the like. A temperature distribution may be generated in the fuel cell stack 11, but it is necessary to set all the cells 10 in the fuel cell stack 11 to 100 ℃. In the present invention, the operating temperature of the fuel cell 10 may be 100 ℃ or higher, preferably 105 ℃ or higher, more preferably 110 ℃ or higher, and still more preferably 115 ℃ or higher. The upper limit of the operating temperature of the fuel cell 10 is usually set to 150 ℃ or lower, preferably 140 ℃ or lower, and more preferably 130 ℃ or lower. As the upper limit value and the lower limit value of the operating temperature, any temperature may be combined.
Hydrogen gas as fuel gas is stored in the hydrogen tank 18. The hydrogen gas is supplied from the hydrogen tank 18 to the compressor 13a via the hydrogen gas supply pipe 6 c. In the compressor 13a, the hydrogen gas is compressed and pressurized. The pressurized hydrogen gas is supplied to the humidifier 12a. At this time, the hydrogen gas is humidified to have a relative humidity of 70% or more with respect to the temperature of the fuel cell unit 10, and the temperature of the hydrogen gas is set to be the same as or heated to a temperature higher than the dew point corresponding to the amount of humidification. It is confirmed that the humidity of the hydrogen gas is set to a predetermined humidification amount by the humidity sensor 16. The humidified hydrogen gas is then supplied from the hydrogen gas supply port of the fuel cell stack 11 to the inside of the fuel cell stack 11, and is supplied to the anode separator 5a of each fuel cell (fig. 3).
The hydrogen gas 6 that is not used in the fuel cell unit is discharged from the hydrogen gas discharge port of the fuel cell stack 11 via the hydrogen gas discharge pipe 6 d. At this time, the back pressure of the hydrogen gas measured at the outlet of the fuel cell stack was set to 330kPa or more. The back pressure of the hydrogen gas can be measured by a pressure sensor 17 provided in the hydrogen gas discharge pipe 6d, and can be adjusted to a predetermined back pressure by the compressor 13a and the back pressure valve 14 a.
On the other hand, air as an oxidizing gas is introduced from the air inlet port and supplied to the compressor 13b through the air supply pipe 7 c. In the compressor 13b, the air is compressed and pressurized. The high-pressure air is supplied to the humidifier 12b. At this time, the air is humidified so that the relative humidity with respect to the temperature of the fuel cell unit 10 becomes 70% or more, and the temperature of the air is set to be the same as or heated to a temperature higher than the dew point corresponding to the amount of humidification. Further, it is confirmed that the humidity of the air is set to a predetermined humidification amount by the humidity sensor 16. The humidified air is then supplied from the air supply port of the fuel cell stack 11 to the inside of the fuel cell stack 11, and is supplied to the cathode separator 5b of each fuel cell (fig. 3).
The air 7 that is not used in the fuel cell unit is discharged from an air discharge port of the fuel cell stack 11 via an air discharge duct 7 d. At this time, the back pressure of the air measured at the outlet of the fuel cell stack was set to 330kPa or higher. The back pressure of the air can be measured by a pressure sensor 17 provided in the air discharge pipe 7d, and can be adjusted to a predetermined back pressure by the compressor 13b and the back pressure valve 14 b.
In the fuel cell stack 20, heat is generated by power generation of the fuel cells. In order to recover this heat, a coolant is supplied into the fuel cell stack 20 by the circulation pump 19. The cooling water supplied into the fuel cell stack 20 recovers heat via a cooling plate (not shown) or the like disposed between the fuel cells 10 and is discharged to the outside of the fuel cell stack 20 as warm water. The recovered waste heat can be further effectively utilized.
That is, in the present invention, when the fuel cell is at a high temperature of 100 ℃ or higher during operation, the relative humidity of the supply gas is set to 70% or higher, whereby it is possible to supply water vapor in an amount capable of appropriately humidifying the membrane electrode assembly, particularly the electrolyte membrane. Further, even when the pressure of the water vapor increases, a sufficient amount of the reaction gas can be supplied to the electrode of the membrane electrode assembly by increasing the back pressure of the supplied gas to a predetermined value or more. This can improve the catalytic activity and the heat removal efficiency, and suppress an increase in the proton conduction resistance of the electrolyte membrane and the substance diffusion resistance in the electrode reaction, thereby improving the performance of the fuel cell.
During operation of the fuel cell, in the fuel cell unit 10 (fig. 3), hydrogen gas 6 is supplied to the anode side, and air or oxygen gas 7 is supplied to the cathode side. The hydrogen gas is reduced at the anode electrode to generate protons and electrons, and the protons conducted through the electrolyte membrane and the electrons conducted through the external circuit react with oxygen at the cathode electrode to generate water. The consumption amounts of hydrogen and oxygen at the anode electrode and the cathode electrode are in direct proportion to the amount of current flowing through an external circuit, and when the hydrogen and oxygen supplied to the vicinity of the electrodes are insufficient, the hydrogen and oxygen become a factor of reducing the performance as substance diffusion resistance.
As described above, water in the membrane contributes to proton conduction in the solid polymer electrolyte, and the conductivity thereof depends on the water content of the membrane. When the amount of moisture in the membrane is reduced due to a decrease in the humidity in the supply gas or an increase in the operating temperature, the proton conduction resistance increases, causing a decrease in performance. Therefore, in order to obtain a high-performance fuel cell, it is necessary to appropriately control the amounts of hydrogen, oxygen, and water in the supply gas.
In a high temperature range of 100 ℃ or higher, the dehydration rate from the electrolyte membrane is high, and it is necessary to supply a high-humidity gas in order to maintain the water content in the membrane. Specifically, in the present invention, the increase in proton conduction resistance can be suppressed by setting the relative humidity of at least one of the air or oxygen supplied to the cathode side and the hydrogen supplied to the anode side of the fuel cell to 70% or more, preferably 75% or more, more preferably 80% or more, and still more preferably 85% or more.
On the other hand, in a high temperature region of 100 ℃ or higher, the saturated water vapor pressure becomes very large as compared with a temperature region of 100 ℃ or lower, and therefore, the water vapor partial pressure becomes very large in order to keep the humidity in the gas the same as in the temperature region of 100 ℃ or lower. Even under such conditions, the back pressure of the supply gas needs to be set to a predetermined value or more in order to supply hydrogen and oxygen necessary for the electrode reaction. Specifically, in the present invention, by setting the back pressure to 330kPa or higher, preferably 350kPa or higher, more preferably 370kPa or higher, and even more preferably 390kPa or higher, an increase in substance diffusion resistance of the anode and the cathode can be suppressed even in a high current density region.
In particular, the operation method of the present invention is effective when the gas supplied to the cathode side is air. When the supply gas to the cathode side is air, the oxygen concentration in the supply gas is reduced to about 1/5, and therefore the amount of oxygen in the vicinity of the electrode is likely to be reduced. Even in such a situation, by increasing the gas supply pressure to 330kPa or more, a sufficient amount of oxygen gas can be supplied to the cathode electrode, and a high-performance fuel cell can be obtained.
Examples
The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.
[ Synthesis of electrolyte Membrane ]
[ Synthesis example 1]
Synthesis of 2, 2-bis (4-hydroxyphenyl) -1, 3-dioxolane (K-DHBP) represented by the following general formula (G1)
Figure BDA0003863314970000171
49.5g of 4,4' -dihydroxybenzophenone, 134g of ethylene glycol, 96.9g of trimethyl orthoformate and 0.50g of p-toluenesulfonic acid 1 hydrate were charged into a 500ml flask equipped with a stirrer, a thermometer and a distillation tube and dissolved. Then, the resulting solution was stirred at 78 to 82 ℃ for 2 hours. Further, the internal temperature was gradually raised to 120 ℃ and the reaction was heated until the distillation of methyl formate, methanol and trimethyl orthoformate was completely stopped. After the reaction solution was cooled to room temperature, the reaction solution was diluted with ethyl acetate, and the organic layer was washed with 100ml of a 5% potassium carbonate aqueous solution, followed by liquid separation and solvent removal by distillation. 80ml of methylene chloride was added to the residue to precipitate crystals, which were then filtered and dried to obtain 52.0g of 2, 2-bis (4-hydroxyphenyl) -1, 3-dioxolane. GC analysis of the crystals gave 99.8% of 2, 2-bis (4-hydroxyphenyl) -1, 3-dioxolane and 0.2% of 4,4' -dihydroxybenzophenone.
[ Synthesis example 2]
Synthesis of 3,3 '-disulfonic acid sodium-4, 4' -difluorobenzophenone represented by the following general formula (G2)
Figure BDA0003863314970000181
109.1g of 4,4' -difluorobenzophenone (1245012523\\ 125228312481reagent) was mixed in 150mL of oleum (50% so 3 ) (and Wako Junyaku reagent) for 10 hours. Then, the reaction product was gradually poured into a large amount of water, neutralized with NaOH, and then 200g of common salt was added to precipitate the resultant. The resulting precipitate was filtered, and recrystallized from an aqueous ethanol solution to obtain sodium 3,3 '-disulfonate-4, 4' -difluorobenzophenone represented by the above general formula (G2). The purity was 99.3%. The structure was confirmed by 1H-NMR. For impurities passing through capillary tubeElectrophoresis (organic) and ion chromatography (inorganic) were performed for quantitative analysis.
[ Synthesis example 3]
Synthesis of a polyether ketone Polymer electrolyte Membrane comprising a Polymer represented by the following general formula (G5)
Figure BDA0003863314970000191
Using 6.91G of potassium carbonate, 7.30G of 4,4' -difluorobenzophenone (G2) as 3,3' -disulfonic acid sodium having an ionic group obtained in the above synthesis example 2 and 10.3G of 2, 2-bis (4-hydroxyphenyl) -1, 3-dioxolane (G1) having a hydrolyzable group obtained in the above synthesis example 1 and 5.24G of 4,4' -difluorobenzophenone, polymerization was carried out in N-methylpyrrolidone (NMP) at 210 ℃.
A25 wt% N-methylpyrrolidone (NMP) solution in which the obtained block copolymer was dissolved was filtered under pressure through a glass fiber filter, and then the resulting solution was cast on a glass substrate, dried at 100 ℃ for 4 hours, and then heat-treated at 150 ℃ under nitrogen for 10 minutes to obtain a polyketone film. The solubility of the polymer is very good. The membrane was immersed in a 10 wt% aqueous solution of sulfuric acid at 95 ℃ for 24 hours to carry out a proton exchange and deprotection reaction, then immersed in a large excess of pure water for 24 hours, and sufficiently washed to obtain a polymer electrolyte membrane. The softening temperature of the resulting polymer electrolyte membrane was measured by dynamic viscoelasticity measurement, and the result was 160 ℃. The obtained polymer electrolyte membrane had an oxygen gas transmission coefficient of 4.5X 10 at 90 ℃ and 80% RH -11 cm 3 ·cm/cm 2 Sec cmHg, hydrogen gas permeability coefficient of 5.6X 10 -10 cm 3 ·cm/cm 2 ·sec·cmHg。
[ production of Membrane electrode Complex ]
[ example 1]
A transfer sheet (size: 50X 50 mm) with an anode catalyst and a transfer sheet (size: 50X 50 mm) with a cathode catalyst were placed on both sides of the polyether ketone polymer electrolyte membrane (thickness: 10 μm, size: 70mm X70 mm) produced in synthetic example 3, and heated and pressed at 160 ℃ and 4.5MPa for 5min to produce a catalyst layer-coated electrolyte membrane (CCM). As the anode catalyst and the cathode catalyst, a platinum group catalyst supported on a carbon support was used.
As shown in FIG. 1 (cross-sectional view), an anode gas diffusion layer 1a (size: 50 mm. Times.50 mm) and a cathode gas diffusion layer 1b (size: 50 mm. Times.50 mm) were disposed on both sides of the CCM produced above. As the anode gas diffusion layer 1a and the cathode gas diffusion layer 1b, a layer in which a microporous layer containing PTFE and carbon black was formed on a porous carbon sheet ("TGP-H-060" manufactured by toray) was used. The membrane electrode assembly was prepared by hot pressing at 160 ℃ for 5 minutes and under 4.5 Ma.
[ example 2]
An anode catalyst layer 2a was formed on the surface of the anode gas diffusion layer 1a on which the microporous layer was formed, and an anode electrode as a Gas Diffusion Electrode (GDE) was produced. Further, a cathode catalyst layer 2b was formed on the surface of the cathode gas diffusion layer 1b on which the microporous layer was formed, and a cathode electrode as a Gas Diffusion Electrode (GDE) was produced. As the anode gas diffusion layer 1a, the cathode gas diffusion layer 1b, the anode catalyst, and the cathode catalyst, the same ones as in example 1 were used. As shown in FIG. 2 (cross-sectional view), the anode electrode (dimension: 50 mm. Times.50 mm) and the cathode electrode (dimension: 50 mm. Times.50 mm) were disposed on both sides of the polyether ketone polymer electrolyte membrane (thickness: 10 μm, dimension: 70 mm. Times.70 mm) produced in Synthesis example 3. The membrane electrode assembly was hot-pressed at 160 ℃ for 5 minutes and 4.5Ma to prepare a membrane electrode assembly.
[ evaluation of high-temperature Power Generation (Power Generation Performance) ]
The membrane electrode composite produced by the methods described in examples 1 and 2 was set in a JARI standard cell "Ex-1" (electrode area 25cm 2) manufactured by UK and K.K.) as a module for power generation evaluation. Hydrogen gas is supplied as a fuel gas to one anode electrode, and air is supplied as an oxidizing gas to the other cathode electrode. The power generation evaluation was performed under the following conditions, and the current was swept from 0A/cm 2 to 1.2A/cm2 until the voltage was 0.2V or less. In the present invention, the voltage at a current density of 1A/cm2 was compared. Further, when the membrane electrode assembly is disposed in the above-described cell, a pressure of 0.7GPa is applied.
An electronic load device: electronic load device manufactured by Chrysanthemum Water electronics Industrial Corp, PLZ664WA "
Cell temperature: 65 deg.C, 120 deg.C
Gas humidification conditions (hydrogen and air): 60% RH, 90% RH
Gas back pressure (hydrogen and air): 200kPa, 330kPa
Gas utilization rate: the anode was 70% of the metered amount and the cathode was 40% of the metered amount.
The measurement results are shown in table 1 below.
Figure BDA0003863314970000211
It is understood from the table that the voltage drop occurred in the membrane electrode assemblies of examples 1 and 2 under the conditions of the relative humidity of 60% and the gas back pressures of 200kPa and 330kPa when the operating temperature was increased from 65 ℃ to 120 ℃. On the other hand, under the condition of a relative humidity of 90%, the voltage does not decrease even when the operating temperature is increased from 65 ℃ to 120 ℃, and good performance exceeding 65 ℃ is obtained under the condition of a back pressure of 330 kPa.
[ evaluation of high-temperature Power Generation (humidity dependence) ]
The membrane electrode assembly produced by the method described in example 1 was set in a JARI standard cell "Ex-1" (electrode area 25cm 2) manufactured by Yinghe corporation, and used as a module for power generation evaluation. Hydrogen gas is supplied as a fuel gas to one anode electrode, and air is supplied as an oxidizing gas to the other cathode electrode. The power generation evaluation was carried out under the conditions that the voltage when the humidity was changed from 30% RH to 95% RH was compared while maintaining the current density of 1A/cm 2. Further, when the membrane electrode assembly is disposed in the above-described cell, a pressure of 0.7GPa is applied.
An electronic load device: electronic load device "PLZ664WA" manufactured by Chrysanthemum Water electronics industries Ltd "
Cell temperature: 120 deg.C
Gas humidification conditions (hydrogen and air): 30% RH-95% RH
Gas back pressure (hydrogen and air): 330kPa
Gas utilization rate: the anode was 70% of the metered amount and the cathode was 40% of the metered amount.
The measurement results are shown in table 2 below.
Figure BDA0003863314970000231
As is apparent from the table, the membrane electrode assembly of example 1 exhibited a voltage rise of 1A/cm2 as the relative humidity rises under the conditions of an operating temperature of 120 ℃ and a back pressure of 330 kPa. The voltage has a high humidity dependence when the cell is treated to 30-60% RH, while the voltage has a low humidity dependence when the cell is treated to 70% RH or more, and stable and high power generation performance can be achieved by treating the cell to 70% RH or more.
Description of the figures
1a: anode gas diffusion layer
1b: cathode gas diffusion layer
2a: anode catalyst layer
2b: cathode catalyst layer
3: electrolyte membrane
4: membrane Electrode Assembly (MEA)
5a: anode separator
5b: cathode separator
6: hydrogen gas
6c: hydrogen gas supply pipe
6d: hydrogen gas discharge pipe
7: air (a)
7c: air supply pipe
7d: air outlet pipe
10: fuel cell unit
11: fuel cell stack
12a, 12b: humidifier
13a, 13b: compressor with a compressor housing having a discharge port
14a, 14b: back pressure valve
15: temperature sensor
16: humidity sensor
17: pressure sensor
18: hydrogen tank
19: cooling liquid circulating pump
20: fuel cell system

Claims (11)

1. A method for operating a fuel cell including a membrane electrode assembly having an electrolyte membrane, a catalyst layer, and a gas diffusion layer, the method comprising a step of setting an operating temperature of the fuel cell to 100 ℃ or higher, wherein a relative humidity of a supply gas supplied to the fuel cell is set to 70% or higher, and a back pressure of the supply gas is set to 330kPa or higher.
2. The method of operating a fuel cell according to claim 1, wherein the supply gas is air or oxygen supplied to a cathode side of the fuel cell, and/or hydrogen supplied to an anode side of the fuel cell.
3. The method of operating a fuel cell according to claim 2, wherein the supply gas is air supplied to a cathode side of the fuel cell.
4. The method of operating a fuel cell according to any one of claims 1 to 3, wherein the electrolyte membrane contains a solid polymer electrolyte.
5. The method of operating a fuel cell according to claim 4, wherein the solid polymer electrolyte contains a proton conductive polymer.
6. The method for operating a fuel cell according to claim 5, wherein the proton conductive polymer is a hydrocarbon polymer.
7. The method for operating a fuel cell according to any one of claims 1 to 6, wherein the softening temperature of the electrolyte membrane is 120 ℃ or higher.
8. The method for operating a fuel cell according to any one of claims 1 to 7, wherein the electrolyte membrane has an oxygen transmission coefficient of 1.0 x 10% at 90 ℃ and 80% RH -9 cm 3 ·cm/cm 2 Sec cmHg or less.
9. The method for operating a fuel cell according to any one of claims 1 to 8, wherein the hydrogen gas permeability of the electrolyte membrane is 5.0 x 10% at 90 ℃, 80% RH -9 cm 3 ·cm/cm 2 Sec cmHg or less.
10. The method for operating a fuel cell according to any one of claims 1 to 9, wherein the catalyst layer contains an oxide support.
11. A fuel cell system used in the fuel cell operation method according to any one of claims 1 to 10, the fuel cell system including a fuel cell having a membrane electrode assembly including an electrolyte membrane, a catalyst layer, and a gas diffusion layer, a humidifier for humidifying supply gas to be supplied to the fuel cell, and a compressor for raising a back pressure of the supply gas.
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